Elimination of Indigenous Measles--United States

An effort is underway to eliminate indigenous measles* from the United States; a target date of October 1, 1982 has been set (1). This article summarizes the successes of that effort and the current measles situation in the United States.

The measles elimination strategy has three major aspects: achievement and maintenance of high immunization levels, development of strong and effective surveillance systems, and aggressive response to the occurrence of disease. Implementation of this strategy has involved numerous private agencies, professional organizations, teachers, parents, and students, as well as governmental agencies at all levels.

All states now have laws requiring measles immunization as a condition of first entry to school; in 40 states and the District of Columbia, these laws extend to all grade levels (kindergarten through 12th grade). In the fall of 1981, the national measles immunization level was 97% for children entering kindergarten or first grade for the first time. Every state has strengthened its surveillance systems; in 43 states, active surveillance systems in which health departments regularly contact health care providers likely to see suspected cases of measles have been instituted. Suspected cases of measles are usually investigated within 24 hours of notification. Routine aggressive responses to suspected cases and outbreaks include rapid identification of susceptibles, provision of vaccination services, and the exclusion of susceptibles from school.

To reduce the importation of measles into this country, all offices issuing United States visas abroad currently provide information on the importance of assuring measles immunization. Although no vaccination requirement currently exists for entry into the United States, visa applicants are advised that children cannot enter school in the United States without proof of immunization. The U.S. Armed Services have instituted a policy of routinely vaccinating susceptible recruits against measles.

These program elements are largely responsible for the marked progress that has been made to date (Table 1, Figure 1). Impressive declines have been seen in the reported occurrence of measles. The number of measles cases reported in the first 37 weeks of 1982 is 3% of the number reported in the same period of 1977 and 0.3% of the number reported during the same period of 1962 (the year before measles vaccine was introduced). For the past 66 weeks, 100 cases per week have been reported.** By contrast, in no year before 1977 had 100 cases per week been reported for as many as 10 weeks.

Just as the overall number of measles cases has declined dramatically, so has the geographic extent of measles in the United States (Table 2). Only 10% of the nation's counties reported measles at any time during 1981, and provisional data indicate that only 5.3% of counties have reported measles thus far in 1982, suggesting that indigenous transmission has been eliminated from most of the United States.

Increasing effort is being made to identify the source of every reported measles case and to confirm each case serologically or epidemiologically by linkage to other measles cases. In the 12-week period from July 3 through September 24, 1982, a source was identified for 57% of the measles cases provisionally reported, and 23% of the cases have been confirmed serologically.

In 1982, imported measles cases have been reported at a rate of approximately 2.5 cases per week; most have resulted in little or no secondary spread. During the past 12 weeks, there were 33 imported cases--only 3 of which resulted in any identified secondary spread.** In May and June, however, a measles outbreak occurred in Duchess and Ulster Counties, New York, with 89 cases linked to a student who had traveled to the U.S.S.R. with his high school class. Since such importations are likely to continue, they will challenge the maintenance of measles-free status in the United States, necessitating the continued maintenance of high immunization levels and aggressive surveillance systems and responses to the occurrence of suspected cases. Sporadic cases of measles-like illness in which neither an apparent source nor spread can be identified will also continue and must be investigated promptly with efforts made to confirm the diagnosis serologically.

The exact date of the elimination of indigenous measles transmission from the United States will only be known in retrospect. Currently, only 3 chains of transmission are known to exist, one of which involves four states.** With the interruption of these last indigenous chains, future measles cases in the United States should be related to measles importations from other countries. Reported by Immunization Div, Center for Prevention Svcs, CDC.

Reference

1. CDC. Goal to eliminate measles from the United States. MMWR 1978;27:391. **provisional information *A measles case that occurrs within the United States and cannot be related to an imported case or a measles case that occurrs more than two generations after an imported case to which it is epidemiologically linked.

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